1. Field of the Invention
The present invention relates to straddle-type vehicles, and more particularly, to straddle-type vehicles with a rear frame extending from a main frame rearwardly with respect to the vehicle.
2. Description of the Related Art
Straddle-type vehicles include a main frame extending in top-to-bottom and front-to-rear directions with respect to the vehicle for supporting the engine, and a rear frame extending from the main frame rearwardly with respect to the vehicle. Typically, a rear frame must have a sufficient strength in order to provide a basic framework of a rear portion of the vehicle.
For example, the straddle-type vehicle disclosed in JP 2012-35714 A includes a rear frame composed of a seat pipe supporting the seat and a lower pipe located lower than the seat pipe for supporting the seat pipe. The seat pipe and the lower pipe each have one end connected with the main frame, while the other end of the seat pipe is connected with the other end of the lower pipe. The one end of the lower pipe is connected with the main frame at a location lower than the connection point between the one end of the seat pipe and the main frame.
In such an arrangement with a rear frame having a seat pipe (hereinafter referred to as upper frame) and lower pipe (hereinafter referred to as lower frame), the location where the upper frame is connected with the main frame must be sufficiently spaced apart in a top-to-bottom direction from the location where the lower frame is connected with the main frame in order to ensure a sufficient strength of the rear frame. Thus, the position of the lower frame as measured in a top-to-bottom direction relative to the upper frame is subject to constraints dictated by the desired strength of the rear frame. As such, the freedom of design of the rear frame is low.
Typically, a silencer is attached to the rear frame. For example, at least part of the silencer of an off-road vehicle is located below the rear frame in order to concentrate the mass of the vehicle as measured in a vehicle width direction and prevent the silencer from contacting the foot of the rider and contacting the rear wheel that swings while the vehicle is traveling. If the silencer is thus located, positioning the silencer closer to the center of gravity of the vehicle in order to concentrate the mass of the vehicle as measured in a front-to-rear direction with respect to the vehicle may cause the silencer to contact the lower frame, which is connected with the main frame lower than the upper frame. Thus, the location of the silencer is restricted by the construction of the rear frame.
Thus, a low freedom of design of the rear frame restricts the location of the silencer and other components, leading to a low freedom of design of the vehicle.